linux-kernel - Re: [PATCH v3 07/15] media: qcom: camss: Capture VFE CSID dependency in a helper function

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Date:   Sat, 26 Aug 2023 13:01:08 +0100
From:   Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>, rfoss@...nel.org,
        todor.too@...il.com, agross@...nel.org, andersson@...nel.org,
        mchehab@...nel.org, hverkuil-cisco@...all.nl,
        laurent.pinchart@...asonboard.com, sakari.ailus@...ux.intel.com,
        andrey.konovalov@...aro.org
Cc:     linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 07/15] media: qcom: camss: Capture VFE CSID dependency
 in a helper function

On 26/08/2023 11:02, Konrad Dybcio wrote:
> On 23.08.2023 12:44, Bryan O'Donoghue wrote:
>>  From sdm845 onwards we need to ensure the VFE is powered on prior to
>> switching on the CSID.
> And what's the symptom if we fail to ensure this? How can someone
> adding support for another platform tell whether the match-list
> should be expanded?

That person has to understand the dependency.

The first version of this patch >= SDM845 would mitigate needing to know 
to expand the list.

Rather than revisit that discussion, I will amend the commit log.

> 
>>
>> Alternatively we could model up the GDSCs and clocks the CSID needs
>> without the VFE but, there's a real question of the legitimacy of such a
>> use-case.
>>
>> For now drawing a line at sdm845 and switching on the associated VFEs is
>> a perfectly valid thing to do.
>>
>> Rather than continually extend out this clause for at least two new SoCs
>> with this same model - making the vfe_get/vfe_put path start to look
>> like spaghetti we can encoded the dependency in a helper function.
>>
>> Use csid_depends_vfe() for this purpose.
>>
>> Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
>> ---
>>   .../media/platform/qcom/camss/camss-csid.c    | 20 +++++++++++++++++--
>>   1 file changed, 18 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/media/platform/qcom/camss/camss-csid.c b/drivers/media/platform/qcom/camss/camss-csid.c
>> index 08991b070bd61..fd04ed112b564 100644
>> --- a/drivers/media/platform/qcom/camss/camss-csid.c
>> +++ b/drivers/media/platform/qcom/camss/camss-csid.c
>> @@ -146,6 +146,22 @@ static int csid_set_clock_rates(struct csid_device *csid)
>>   	return 0;
>>   }
>>   
>> +static bool csid_depends_vfe(u32 version)
> toggle_vfe_before_csid?

If that's clearer np.

>> +{
>> +	bool ret = false;
>> +
>> +	switch (version) {
>> +	case CAMSS_845:
>> +	case CAMSS_8250:
>> +		ret = true;
>> +		break;
>> +	default:
>> +		break;
>> +	}
>> +
>> +	return ret;
> I'm not sure if it would be okay with like C conventions and
> stuff, but this can be made shorter by returning from within
> the switch statement

Yes but you still need the explicit return at the end of the function or 
from memory at least some of the compiler/static analysis or checkpatch 
stuff - I forget which - will complain.

---
bod